A modified bis(thioacetoxy)aurate electron microscopic histochemical method for acetylcholinesterase (AChE) and pseudocholinesterase (ChE) will be used to determine the cytological distributions of these enzymes in autonomic ganglia, the carotid body, skeletal muscle, placenta, smooth muscle, and other sites. Pharmacological experiments will be performed to elucidate the physiological roles of acetylcholine (ACh) and AChE in these tissues. The mechanism of the neurotrophic influences on the development and maintenance of trans-synaptic AChE will be investigated with the rat superior cervical ganglion. The localization of cholinergic receptors will be investigated by means of electron-dense affinity labeling agents.